Supplementation will be discontinued and infant will exit the study if surgical necrotizing enterocolitis/bowel perforation is diagnosed, if 25 (OH)D concentrations >60ng/mL (>150nmol/L; potentially toxic) are detected or, if infant NPO for greater than 24 hours. If infant made briefly NPO (<24h) for feeding intolerance, suspected sepsis, hypotension,hemodynamically significant PDA, or respiratory difficulties, enteral vitamin D will not be discontinued.